The present invention is a very low cost method to insert and extract heat energy to and from potable water using a single pre-existing underground water service pipe, without either consuming or degrading the potable water. Extremely efficient geothermal heat pump space-conditioning installations are made possible without the high cost of excavation or insertion of underground heat exchanger equipment. When combined with on-site fuel cell electrical power and co-generation waste heat, the present geothermal invention becomes even more efficient, consuming only a small fraction of the energy required by prior art systems.
The high energy efficiency of geothermal heat pump (GHP) air conditioning is well known. Geothermal renewable energy is dilute, in terms of energy density, but it is still the world""s most abundant and most reliable form of stored terrestrial clean energy. The dilute thermal energy density at the surface of the earth compared to many other high energy density sources (such as fossil fuels) makes the immense geodetic heat sink difficult and expensive to access. Despite its dilute energy density, the earth contains far more stored energy than all other conventional energy sources combined. Hence, the pursuit of geodetic clean energy remains a high priority and is completely justified. Unfortunately, its current use hardly registers on the global energy-usage scale for the following reasons. Prior art GHP installations are too expensive; GHP installation-payback is not cost efficient for many years. Prior art GHP systems are also not universally appropriate for all ground conditions such as poor thermal conduction, soil hardness (rock), lack of moisture, and high population density zones (high-rises for example) which do not offer high acreage to tap ground heat. Deep boring and/or long trenching costs represent about half the total cost in a typical geothermal installation, but excavation costs can be much greater in many locations. Geothermal publications abound with sophisticated schemes to drill deep geothermal holes for the insertion of closed fluid loops, back-filled with improved thermal conduction grouting materials. Likewise, the literature overflows with techniques for filling long deep trenches with various thermally conductive loop backfill materials. Even navigationally guided horizontal loop-drilling technology has been developed to drill very long curved loops, where tubing can be pulled into and around a horizontal drilled loop. Furthermore, numerous techniques have been developed to tap the geothermal energy of lakes, rivers, and oceans. Single well (open loop) and multiple well (closed loop) ground water sources have also been exploited, but the use of such geothermal bodies of water still imposes high installation and excavation costs, or longevity shortcomings such as dirt and/or debris filtration problems, and a long list of similar objections.
In other attempts to bring geothermal costs down, elaborate compound geothermal heat exchange systems are being employed. For example, noisy evaporative cooling water towers have been combined with cool ground waters. The cost can be high in large commercial applications, but energy savings are also high. Another high cost example of commercial size geothermal installationsxe2x80x94typically in excess of 100-1000 tons (1,200,000 to 12,000,000 BTU/hr)xe2x80x94involves major excavation to access municipal water mains at distant points. Major municipal water flow is interrupted and then diverted with two large pipes directed too and from a large heat exchanger device, forming a large underground ioop within a municipal water system. This type of costly installation requires large earth moving machines for significant earth (and even paved road) excavation, followed by land and road restoration and, of course, the costly permits to interrupt large commercial water mains. Such prior art heat exchange systems claim to be cost effective only in large multi-dwelling housing developments of 40 or more adjacent homes, or in large commercial buildings. The amount of excavation for this special type of geothermal application is high, but can be less costly than excavating many thousands of feet of individual underground heat exchange closed loops for an entire housing development. Such community geothermal installations have additional complex and expensive considerations, such as measuring and metering the thermal usage billed to each dwelling or office connected to the common municipal water system. The many limitations of massive evacuation for heat exchange loops in municipal water mains makes the cost of such complex geothermal methods prohibitive for single residences.
Nonetheless, the availability of effectively inexhaustible stored geothermal energy, the low pollution associated with it, and the low energy cost of using it, continues to beckon us to adopt this largest-of-all renewable clean energy sourcesxe2x80x94especially if installation costs can be greatly reduced, as disclosed in the present invention.
There is no question that xe2x80x9crenewablexe2x80x9d geothermal energy is extremely clean, incredibly abundant, essentially free, energy-efficient, and exceptionally reliable 24 hours a day (unlike wind, tide, or solar energy). The temperature of the few hundred outermost feet of the earthxe2x80x94that which is accessed for GHPxe2x80x94is largely governed by years of stored solar energy. In fact, more sunlight energy intersects this planet in one year than all the energy used by mankind throughout history. In that respect, GHP is really just a convenient form of stored solar energy, just as wind and rain energy are byproducts of intercepted solar energy. Geothermally stored solar energy is simply a much more direct solar absorption and heat storage mechanism. High temperature heat energy from deep within the earth""s core conducts through the earth""s crust and is ultimately liberated from the surface of the earth at a rate of only 15.9 BTUs per hour per square foot. Solar energy heating the earth exceeds 100 watts/ft2, or more than 341 BTUs per hour per square foot, so that incoming solar energy far exceeds the heat losses from the earth""s core. The earth""s crust has reached an equilibrium average temperature resulting from daily solar exposures and seasonal variations, so xe2x80x9cgeothermal energyxe2x80x9d is better referred to as xe2x80x9cgeo-solar energyxe2x80x9d. When that stored solar energy is tapped by geothermal heat pumps, the stored solar energy store is temporarily borrowed in the winter months and is pumped back in the summer months. The highest core temperature of the earthxe2x80x94xe2x80x9cgenuine geothermal energyxe2x80x9d, is typically extracted for steam powered electric generators in western territories of the U.S. Unlike other clean renewable solar energy systems (e.g. solar photoelectric arrays), which require massive and very costly man-made energy storage systems when no sunlight is present, xe2x80x9cgeothermal stored solar energyxe2x80x9d is cost free and essentially unlimited year round. Until now, the main obstacle has been that of their high costs of excavation for heat exchange loops.
The principle obstacles to the global adoption of prior art GHP have been the high installation cost and the accompanying long energy-savings payback period. The U.S. government""s Department of Energy (DOE) endorses the adoption of various geothermal energy systems and has a goal of increasing geothermal installations to only 2 million by 2005. The DOE also endorses renewable solar energy installations with a similar low target of only 1 million roofs with solar panels by 2010. However, both of these very modest goals reveal how reluctant Americans are to adopt the costly prior art clean energy saving technologies. If geothermal installation costs could be greatly reduced immediately (as with the present invention), and if the ground itself were more universally conducive to geothermal deployment (as achieved by the present invention), then geothermal energy would likely become a much more popular clean energy source far sooner than authorities presently forecast. Cheap clean energy is not just desirable, it""s a global urgency. Unlike solar renewable energy, which requires enormous energy storage facilities during prolonged zero-sunlight periods, the geothermal heat sink is available at all places, at all times.
Much more aggressive DOE and EPA goals of perhaps 20 to 50 million geothermal installations (a 50 to 125-fold higher target) by 2010 would significantly register on the national energy scale as well as on greenhouse emission reductions. Unfortunately, the nation would be hard pressed to absorb the resulting installation costs. However, if geothermal installations were less expensive and less limiting, then more aggressive and worthy goals of even more than 50 million installations would be practical. Such a goal would significantly impact national and global greenhouse objectives. Moreover, if geothermal energy can be made far more cost effective, then it follows that other nations might be eager to adopt it as well.
As will be shown by the present invention, far lower geothermal installation costs, more universal installations, and much higher geothermal efficiencies (than prior art geothermal systems), are now possible. It is estimated that as many as 500 million to one billion dwellings worldwide could readily adopt inexpensive geothermal energy through the application of the present invention, and this would result in a host of benefits to the environment and to the global economy.
An existing underground, geothermal heat exchange, potable water infrastructure already exists which is capable of transporting, delivering, and absorbing ample heat energy to and from buildings using a reciprocating potable water flow to and from dwellings within a single municipal water supply pipe in accordance with the present invention. The present invention uniquely exploits this existing municipal geothermal infrastructure without interrupting, impeding, consuming, or degrading valuable potable water.
The present invention proposes to temporarily draw and store a sufficient quantity of potable water from water mains, during which storage time, dwelling heat energy is exchanged with a quantity of temporarily stored water. Following the heat exchange period, the potable water, with undiminished purity, is forced backward through the inlet water meter so that the net geothermal water consumption registers a net zero consumption. The key to such a low cost potable water heat exchange system resides in the fact that most, if not all, currently installed water meters are, or can be, 100% flow-reversible. With such a reversible meter, potable water flowing one way and registering a positive usage can also be pumped backward to register an equal but opposite negative usage. Thus, cooled or heated potable water, when forced backward through the dwelling""s bi-directional water metering device, results in no net water usage recorded or billed. However, the usage of xe2x80x9cgeothermal waterxe2x80x9d; that is, the thermal units added to or removed from the potable water, can be measured and can be billed.
The present invention enables the existing underground potable water and sewage infrastructure to serve most of the modern world geothermally, resulting in a rare opportunity to make a cost effective quantum leap in global energy savings, and consequently, a massive reduction in greenhouse emissions without a reduction in the available potable water. Further, once it is known how to cost-efficiently combine the existing potable water infrastructure with the present invention, several other major thermal enhancements also become possible which are not possible with prior art open or closed loop geothermal systems. For example, waste heat from large commercial electric power plants can be thermally coupled into municipal water systems in the winter months, thus raising the potable water temperature delivered to each dwelling and making the heat pump installations of the present invention much more efficient in winter months. Enormous quantities of power plant waste heat could be sold to water companies instead of being released into the atmosphere or nearby bodies of water. Thus, the invention allows low-cost transportation of low-grade (low temperature) power plant waste heat to millions of distant applications. Winter heating, which is a notorious geothermal reduced-efficiency season, can now be made as efficient or even more efficient than summer geothermal cooling. Such increased heat pump winter-efficiency enables the use of even smaller and lower cost individual heat pump systems, while at the same time providing commercial electric power plants and commercial water companies significantly higher profit margins for the wise use of their combined heat energy and existing heat-delivery systems.
In another preferred embodiment of this invention, an on-site fuel cell electric power supply is provided in a dwelling incorporating the potable water geothermal heat pump system of the invention and is incorporated within the system to power the geothermal system as well as supply electric power to the entire dwelling. The electric generation waste heat (e.g. waste fuel cell heat) is used in winter months by the geothermal water-storage system to greatly reduce winter energy consumption. Such on-site co-generation of electricity, heating, cooling, and hot water, makes this unique combination of energy systems far more efficient than prior art heating and cooling systems, makes it the least CO2 polluting, and represents the lowest operating cost installation. It is believed that widespread usage of this invention can meet a large fraction, or even exceed the CO2 reduction goals set by the international Kyoto Accord through conservation, rather than by costly industrial plant modifications.
The key to even hoping to achieve such lofty geothermal installation goals lies almost entirely in three primary objectives of the present invention: 1) installation speed and simplicityxe2x80x94requiring no excavation whatsoever; 2) greatly reduced installation costs; and 3) much higher energy efficiency over prior art geothermal systems. Ideally, an immediate positive cash flow following a geothermal installation should eliminate the final resistance to widespread geothermal installations. If, for example, each geothermal installation cost were low enough so that monthly payments for that installation were less than the monthly energy savings, then a new geothermal system would actually create an immediate net positive cash flow. The possibility of immediate positive cash flow differs from prior art systems, which produce negative cash flow. A very low cost geothermal installation, which is the object of the present invention, is, therefore, capable of removing the final barriers to widespread urban and suburban geothermal usage. As will be shown below, the present invention is far superior in cost-effective payback than prior art geothermal systems, including closed loop and open loop systems, large municipal water underground loop systems, and water tower assisted systems, and is even superior to closed loop wells and lake/pond heat transfer systems.
Almost invisible to most of us, and for well over a century, this nation and much of the rest of the industrialized world have been very busy building an extensive underground municipal water plumbing infrastructure, which is ideal for tapping the immense geodetic heat sink. The U.S. alone has an estimated one million miles of large diameter underground plumbingxe2x80x94all of which can be excellent geothermal heat exchangers, as will be made evident by the present invention. It must be emphasized that potable water is a costly commodity which is becoming scarce, and should definitely not be wasted on geothermal energy applications. The present invention does not waste potable water at all.
Therefore, one key objective of the present invention is a very low cost method to extract/insert heat energy from/to potable water using a single pre-existing underground water service pipe, without either consuming or degrading the potable water. The huge underground infrastructure of existing potable water plumbing is used to extract immense geothermal energy, and can also cost-effectively tap even more geothermal energy from lakes, rivers and oceans, as well as waste heat from commercial electric power plants. The existing infrastructure is a veritable treasure of nearly free geothermal energy. The present invention teaches general ways that this geothermal energy can be readily tapped and applied to almost any dwelling which is served by commercial water, or served by any source of community potable water, while completely eliminating the expense of digging, drilling, and plumbing the terrain near each building. As will be more fully appreciated below, the present geothermal invention consumes zero additional potable water, as there is no net increase in water usage billing to each geothermal energy user. Relatively small quantities of geothermal potable water are merely briefly xe2x80x9cborrowedxe2x80x9d from the underground water infrastructure, heat energy is then extracted or injected from/to it (depending on cooling or heating needs), and then it is returned to the underground infrastructure as unaltered clean water. Once the xe2x80x9cborrowedxe2x80x9d clean water is returned to the underground main potable water supply, it again naturally equilibrates with the underground average thermal conditions on its way downstream to other geothermal energy users.
Another significant objective of the present invention will be that of using the same existing underground plumbing infrastructure to transport most of the nation""s commercial electric power plant low grade waste heat directly to residential and commercial dwellings, thereby significantly improving geothermal heat pump efficiencies far beyond prior art geothermal heat pump system efficiencies.
Finally, the invention uniquely combines geothermal space conditioning with fuel cell technology to generate low cost on-site electricity while applying the fuel cell waste heat to geothermal winter heating, the latter being impractical with prior art underground geothermal loops.
Commercial electric power companies generally have had a net efficiency of only about 25% because the power plant itself is only 30% efficient in generating electricity and the power distribution grid, with its many transformers, often has only about 90% efficiency. Such a huge waste of energy and liberated CO2 can be almost completely eliminated with on-site electrical power generation. On-site electrical power generation, even if only 40% effective, eliminates the distribution inefficiencies and therefore can be as much as twice as efficient as commercial power systems, and in addition, waste heat from on-site electrical generation can be used at the same site for winter heating and/or for partial hot water generation. Fuel cell technology, for example, is now capable of over 40% efficiency in converting fossil fuels directly into electricity silently and with no moving parts, so fuel cells in combination with the present geothermal invention make an ideal and unique combination which represents a preferred embodiment of this invention.
The very hot core of the earth is slowly cooling through the outermost crust at an average rate of a mere 15.9 BTUs per square foot per hour (4.66 watts/ft2). However, the earth""s surface is also being solar heated half of every day with a much higher energy density of  greater than 100 watts/ft2. Therefore, xe2x80x98geothermal energyxe2x80x99 at the earth""s surface is actually naturally stored solar energy, for the most part. The thin outer geothermal crustxe2x80x94the part which is within relatively easy reach for heat exchangingxe2x80x94typically averages 50 to 70 degrees F. (depending largely on latitude). The shallow ground temperatures tend to equilibrate close to the average annual air temperature (winter/summer) at each latitude. However, very localized abrupt thermal ground conductivity variations (and heat exchange capacity) can occur in earth borings as close as a few feet apart. Some dry soil and rock formations have poor thermal conduction whereas others nearby are excellent, making the effectiveness of conventional geothermal systems unpredictable. A more ideal underground geothermal heat exchange configuration would be a physically large system, such as a municipal water system, wherein flowing water tends to average the various local ground thermal conduction properties. Tapping a large underground potable water infrastructure, as proposed by the present invention, ideally meets that temperature-averaging objective.
Although the stored geothermal energy in the earth is an immense source of energy, it also can be thought of as an immense heat sink for thermal energy storage. Geothermal space-conditioning in accordance with the invention involves the mere xe2x80x9cborrowingxe2x80x9d of geothermal heat energy from the earth in the winter to heat buildings, and returning most of it back to the earth in the summer months. The heat energy which is swapped to and from the earth is xe2x80x9cpumpedxe2x80x9d up a few degrees F. in the winter months to heat dwellings and in the summer months heat is xe2x80x9creverse pumpedxe2x80x9d down a few degrees F., causing the summer heat to flow back into the earth. The key to efficient deployment of geothermal heat exchange as described herein is the phrase xe2x80x9ca few degreesxe2x80x9d. If, for example, the average ground temperature were 60xc2x0 F. in the winter, the geothermal heat must be pumped up a few degrees to maintain a comfortable 75xc2x0 F. indoor temperature (a mere 15xc2x0 F. difference). Under such mild winter conditions, geothermal heat pumps in accordance with the invention would barely be taxed to accomplish that goal. By comparison, prior art air-exchange heat pumps offer much lower efficiency in pumping outdoor winter heat from 10xc2x0 F. outside air up to 75xc2x0 F. indoor temperatures (a 65xc2x0 F. difference). A similar comparison arises in the summer months. If a heat pump must eject heat to the outdoors from a 75xc2x0 F. dwelling to a hot (e.g. 100xc2x0 F.) summer environment, the work performed by an air-to-air heat pump against a 25xc2x0 F. temperature difference is much greater than a geothermal heat pump moving 75xc2x0 F. heat to a cooler 60xc2x0 F. ground temperature. Depending on the heat pump""s electrical efficiency, the local outdoor temperature conditions, and the local geothermal temperature, geothermal assisted heat pumps are much more energy-efficient than common air-exchange heat pumps and many times more efficient than fossil fuel systems. The concepts of extremely high annual efficiency and 24 hour reliability, are the central attractions to all geothermal space conditioning.
However, the previous simplified thermal examples do not reflect reality. The fact is that ground temperatures are not constant year round at 60xc2x0 F. Ground temperatures can vary to lower than 40xc2x0 F. and higher than 80xc2x0 F., depending on depth, season, geographic latitude, and ground thermal conductivity. It is obvious that installations where the ground temperature is very cold (e.g. 40xc2x0 F.) in the winter months, geothermal heat pump systems cannot be as efficient as installations where winter ground temperatures are much higher (the higher, the better when extracting ground heat). Likewise, geothermal installations are not as efficient in locations where the summer ground temperatures are nearly 80xc2x0 F. When injecting heat energy into the ground, the highest geothermal efficiency occurs when the ground temperature is coolest.
For most populated locations, ground temperatures average around 55xc2x0 F. to 80xc2x0 F. in summer months, and prior geothermal installations are very efficient in summer months in these locations. But prior art geothermal systems are not economically attractive nor as energy efficient in winter months for several reasons. When extracting ground heat from cool winter-ground, the surrounding ground gets even colder. If the winter ground temperature is already cold (e.g. 40xc2x0 F. to 55xc2x0 F.) and additional heat energy to heat dwellings is extracted, the ground temperature decreases, making geothermal efficiencies further decrease. For example, if the winter ground temperature were normally 45xc2x0 F., and a geothermal heat pump extracted additional ground heat which lowered the average ground temperature to, for example 35xc2x0 F., then the geothermal system would be inefficiently working against a 45xc2x0 F. to 55xc2x0 F. temperature differential in the winter. Hence, winter geothermal efficiency is lowest when BTU demand is highest. Despite better thermal insulation, residential BTU heat energy needs in the winter may be 10-12 times greater than cooling energy demands in the summer. Although prior art geothermal heat pump installations can be energy efficient, they are least efficient in cold climatesxe2x80x94exactly where heat energy is needed the most. There is an exciting practical solution to this geothermal winter efficiency dilemmaxe2x80x94using winter electricity waste heat to increase geothermal efficiency.
As discussed above, electric power plants exhibit electrical generating efficiency ranging from as low as 30% to as high as 57%, resulting in a great deal of waste heat at the power plant that costs the utilities money to dissipate. Waste heat is low-grade heat, but it must be dissipated year-round, and a major obstacle preventing the wise use of that waste energy has been a lack of a cost effective heat delivery system to consumers. There are many electrical power plants that do sell very small quantities of waste heat to nearby heat consumers, such as steam heat energy for local building space heating. But the lowest grade electric waste heat, which represents the preponderance of electrical power, has never been of any practical value, until now. In accordance with the invention, the electrical power waste heat is cost-effectively delivered in winter months for geothermal heat pumping via the existing underground potable water systems. Prior art geothermal systems with underground heat exchange loops cannot efficiently use commercial waste heat delivered via municipal water systems because most of the waste heat energy would be lost in the ground loop. The present invention has no ground loops nor ground loop loses.
Therefore, another major object of the present invention is a practical and cost-effective method to distribute and employ a large portion of electrical power plant winter waste heat in a form that can dramatically increase winter geothermal heat pump efficiency, while allowing electrical power plants an opportunity to become more profitable by selling waste heat. The net effect of such a wise use of this abundant energy resource is that of greatly reducing energy costs to geothermal end users and further reducing greenhouse emissions. The proposed power plant waste heat delivery system is the existing potable water delivery network.
Likewise, electrical waste heat occurs if fuel cells are used to generate on-site electricity. It has been proposed to use on-site fuel cell waste heat for year-round domestic hot water. However, if the electricity demand happens to be low, then the hot water production will be insufficient in that dwelling. Fuel cell waste heat hot water is therefore unreliable. Fuel cell waste heat has never been applied to prior art underground loop geothermal space heating systems because much of the electrical waste heat would be lost to the underground loop heat exchange system. There are several unexpected benefits in applying fuel cell waste heat to the present geothermal invention. For one example, fuel cell waste heat can be fully applied to space heating because space heating has a much larger and continuous demand than hot water. Secondly, the present invention offers no underground loop heat losses. The non-obvious combination of fuel cell co-generation and geothermal heat pumps is a most ideal and efficient marriage and is a highly preferred embodiment of the present invention.
Another source of waste heat available for use with the present invention is found in the discharge of sewer water. The average volume of discharged gray water per household is approximately 200 gallons per day, at an average temperature of 80xc2x0 F. Prior art heating systems do not recover this energy, primarily because the gray water temperature is not high enough; however, the heat pump used with the present invention can recover this energy, for additional and significant energy savings.
The present invention has a large number of unexpected benefits besides the obvious space heating, cooling, and hot water energy efficiencies. To address the full range of geothermal benefits, the basic premise of the invention will be discussed first and the many unexpected benefits will be addressed one by one.